1. Background of the Invention
The present invention relates generally to a multiple-washer nut and, more particularly, to such a nut having a cage for retaining the washers in a tight unitary configuration throughout heat treatment and high tensile use.
2. Description of Related Art
A well received nut construction which provides for self-locking capabilities as well as relatively uniform distribution of load on the nut threads consists of a plurality of conical washers or Belleville washers arranged in stacked relation with their individual openings forming a continuous bore therethrough. A metal enclosure or cage secures the washers in unitary relation. The bore is threaded in conventional manner enabling receipt of a similarly threaded bolt therein. In use, when the multiple washer nut is received on a bolt and brought into pressure contacting relationship with another object (e.g., vehicle wheel) the nut is placed in tension causing the washers to flatten out from their original conical shape and producing a locking action with respect to the bolt. A more detailed description of such a nut can be found in U.S. Pat. No. 4,383,787, FREE SPINNING LAMINATED NUT WITH AUTOMATIC LOCK, by Richard L. Reynolds.
It is a general industry accepted practice as specified both in Society of Automotive Engineers (SAE) and IFI industry requirements that nut strength shear characteristics must exceed bolt tensile strength in order that the failure mode is bolt breakage in all cases. Also, the various nut components including the washers and unitizing outer cage are constructed of a heat treated spring steel. Specifically, soft metal washers are initially stacked and received within a soft outer cage, and final heat tempering is provided after threading.
However, it has been found in a significant percentage of cases, that the outer cage encompassing the nut washers tends to relax its gripping action about the washers during heat treatment which undesirable result is frequently referred to as "blossoming". Such relaxation of the cage with respect to the enclosed washers is deleterious in that it reduces the total amount of shear strength of the nut, as well as producing a shift or misalignment of nut thread pitch which can make bolt installation difficult. Also, where a nut cage has been found to experience a certain amount of blossoming during heat treatment, it also can exhibit further blossoming when in use and exposed to high tensile force with increased deleterious results.